An enlargement lens is used for printing a film image onto a photographic paper by having a magnifying power of 1 or more with enlargement lens mounted on an enlarger. The enlargement lens is used in a dark room for preventing the photographic paper from sensing unnecessary light. Although "safe" lights may be used, the light level is still very low. Therefore, it is difficult to read the stop value scale on the enlarger. This is a requirement such that a suitable stop-value can be determined since it is a condition to be ascertained for having a proper exposure. In view of this need, in the prior art provisions have been made to configure an enlargement lens having a light guide in order to enable stop-value scale illumination by use of the light source in the enlarger. This leads to shortening the operational time in the dark room without extra work and fatigue.
Since, an enlargement lens, generally has a standard magnification in a range of 5.times. to 10.times., the enlargement lens is used not only for the enlargement function but for close-up photography and copying.
However, when a conventional enlargement lens having a light guide for reflecting light inside a lens mount for stop-value scale illumination is used for close-up photography or copying it is possible that light outside the lens mount is sensed on film through the light guide during the actual photographing process. Such an enlargement lens is therefore not practical for multipurpose use and is used only for enlargement.